The present invention relates generally to loading devices that connect to a handle or other user manipulated apparatus on an exercise machine. A wide variety of loading devices, including stacks of iron weights, bundles of bow springs, and various spring and lever systems have been used; yet most fail to provide convenient, finite adjustability of the load delivered. In exercise machines having bow springs, for example, the loading is changed by selecting among a few springs of differing resistance, which is somewhat inconvenient and lacks the advantage of the greater number of finite loads provided by spring and lever systems.
Lever and spring systems also present problems. Since they generally include a non-adjustable spring, the loading is changed by varying the leverage on the spring. It is difficult to conveniently vary the leverage because of the need to simultaneously change the lengths of two legs of the force triangle, without which the result is either (a) the starting position of the exercise is changed or (b) a change in compression or decompression of the spring is experienced. The latter is a particular problem because of the difficulty in making adjustments under spring loads.
One type of prior art device defines one leg of a force triangle as the selected one of a plurality of adjustment positions located along an arc that is equal to the radius of a second leg of the force triangle. With this solution, only a single leg of the force triangle need be changed for loading adjustments. Such an arrangement is shown in U.S. Pat. No. 3,638,941, issued Feb. 1, 1972 to Kulkens, where a coil tension spring is used to provide resistive load to the user. A coil tension spring is, however, generally undesirable because of its high spring rate that results in a rapid increase in loading through the exercise stroke. To reduce the effects of high spring rate, Kulkens preloads the spring in its rest (unactuated) position. But when in the rest position the tension of the preloaded spring forces the exercise arm against a stop and adjustment of the lever arm is still difficult and inconvenient.
U.S. Pat. No. 4,426,077, issued Jan. 17, 1984 to Becker discloses an exercise device that also includes a plurality of adjustment points located along an arc with a radius equal to the length of a preloaded spring leg of the force triangle. Becker addresses the preloaded spring adjustment problem by either (a) locking the spring in a partly extended state and moving the unloaded spring eye between adjustment points or (b) latching the rigid lever arm in a fixed position, and moving the loaded spring eye, via a roller, over the adjustment points. When the desired adjustment point is reached, Becker then either unlocks the spring or retracts the lever arm latch, as the case may be. The method is somewhat inconvenient in that the spring must be locked (or the lever arm latched) while the user is partially through an exercise stroke. Becker does describe a remote cable-actuated latching mechanism for reducing some of the inconvenience.
U.S. Pat. No. 4,684,125, issued Aug. 4, 1987 to Lantz shows a pair of parallelly aligned adjustment plates, each including an arcuately disposed pattern of mating adjustment holes, and a gas compression spring, the extended length of which comprises one leg of the force triangle. A removable pin couples the eye of the compression spring to the selected pair of adjustment holes. The lever arm, which would otherwise collapse when the pin is removed, must be supported by the user during load changes. The eye of the compression spring must also be visually aligned by the user with the desired pair of holes in the adjustment plates. When the pin is inserted through the selected hole pair, the lever arm is again supported by the compression spring. The task of simultaneously supporting the lever arm, aligning the compression spring eye, and inserting the pin is inconvenient, at best and difficult, at worst.